jls@igor.rational.com (Jim Showalter) (03/08/91)
Regarding physiological differences between male/female brains, this
turns out to be largely bogus. There seemed to be some VERY minor
structural differences, but the sample size was quite small and there
has yet to be independent corroboration.
--
***** DISCLAIMER: The opinions expressed herein are my own. Duh. Like you'd
ever be able to find a company (or, for that matter, very many people) with
opinions like mine.
-- "When I want your opinion, I'll beat it out of you."forbes@aries.scs.uiuc.edu (Jeff Forbes) (03/08/91)
In article <jls.667348568@yoda> yoda!jls@igor.rational.com (Jim Showalter) writes: >Regarding physiological differences between male/female brains, this >turns out to be largely bogus. There seemed to be some VERY minor >structural differences, but the sample size was quite small and there >has yet to be independent corroboration. According to _Evolution of the Vertebrate Brain_, the adult human female brain (taking into account body height) is on the average 200 grams less than that of the adult human male brain, using the same scaling. What does this mean? Possibly nothing more than another odd medical statistic. Jeff Forbes "....I have not failed. I've just found 10,000 ways that won't work." Thomas Edison
kim@mathcs.emory.edu (Kim Wallen {Psy}) (03/13/91)
In article <jls.667348568@yoda> yoda!jls@igor.rational.com (Jim Showalter) writes: >Regarding physiological differences between male/female brains, this >turns out to be largely bogus. There seemed to be some VERY minor >structural differences, but the sample size was quite small and there >has yet to be independent corroboration. Jim's comment is relatively accurate in reagrd to Callosal differences in males and females (this difference is not clearly resolved), but it is distinctly incorrect in regard to hypothalamic differences. There is a very clear difference in certain hypothalmic nuclei in male and female humans which develops between 4-6 years of age and continues through adulthood. [reference: Swaab, DF &Hofman, MA 1988 Sexual differentiation of the human hypothalamus: Ontogeny of the sexually dimorphic nucleus of the preoptic area. Developmental Brain Research 44:314-8.] This neural difference is analogous to those reported in rats, guinea pigs, ferrets, and monkeys. It seems this area (which is larger in females than males) is involved in suppressing female sexual behavior in males. When it is lesioned in male rats they now readily show female-like sexual receptivity and initiation. Interestingly in the human study three transsexual males (male to female) all had sexually dimorphic nuclei in the female, but not the male range. Kim Wallen Psychology Department Emory University Atlanta, GA 30322 (404) 727-4125 INTERNET: kim@unix.cc.emory.edu UUCP: {gatech decvax}!emory!kim BITNET: kim@emoryu1
huxtable@kuhub.cc.ukans.edu (Kathryn Huxtable) (03/14/91)
In article <7141@emory.mathcs.emory.edu>, kim@mathcs.emory.edu (Kim Wallen {Psy}) writes: > .... Interestingly in the > human study three transsexual males (male to female) all had sexually > dimorphic nuclei in the female, but not the male range. > This is very interesting. Can this test be performed before death (or non-intrusively)? My main concern with findings like this (valuable though they may be) and with findings concerning sexual orientation and the like is that it isn't clear how much, if any, of human sexuality/gender stuff is determined or influenced by such structures. Our mentation seems to be several orders of magnitude higher than that of rats, so it's not clear that something which is completely determined by some brain difference in rats is also determined the same way in humans (or in all humans). *Any* human behavior seems to be affected by culture and upbringing (though not necessarily by *deliberate* attempts to mold). I suspect that sexual orientation/gender identity/gender roles are much more complex in humans than in any other creature on Earth and that non-human animal studies won't generalize to humans. At best they will indicate directions for research to go. A large potential problem I see with this kind of research, and more importantly with the way it is reported and interpreted, is that when researchers determine that some large percentage of MTF transsexuals have some structure associated with the female pattern rather than with the male pattern, then this can be used to say things like "You're not really transsexual unless you have blah, blah, blah..." The same can be read for sexual orientation. Many gay and lesbian people I know are worried about research into the "causes" of their sexual orientation, because it presumes two things: 1) that their orientation is somehow unnatural and has to have a cause, whereas heterosexuality is normal and has no cause; and 2) that there is just one cause for all cases of homosexuality. (Notice how we slip into the medical mode of speech---gays and lesbians are "cases" and "have something"). We are all people here. We were all born with human genes and raised in human societies. How we turn out is a human phenomenon. I don't see why sexual orientations and gender identities that don't quite fit with the majority's are necessarily pathological. Yet that seems to be the model under which they are studied. Our unconscious biases are the most dangerous, for those are the ones we leave out of account when we try to design controlled experiments. Until an unconscious bias (such as that there are two and only two sexes and everybody is either one or the other. If they aren't, then there's something wrong with them) is brought to our attention, we can't do reasonable research in these areas, because the questions are wrong. When the questions are wrong, the data is usually irrelevant because attention wasn't paid to variables that were not thought to be variables. Etc, etc. ad nauseam.... -- Kathryn Huxtable huxtable@kuhub.cc.ukans.edu
turpin@cs.utexas.EDU (Russell Turpin) (03/14/91)
----- In article <1991Mar8.034313.29112@ux1.cso.uiuc.edu> forbes@aries.scs.uiuc.edu (Jeff Forbes) writes: > According to _Evolution of the Vertebrate Brain_, the adult human > female brain (taking into account body height) is on the average 200 > grams less than that of the adult human male brain, using the same > scaling. What does this mean? Possibly nothing more than another odd > medical statistic. You got it. There is quite a bit of variation in cranium shape, including overall size, overall shape (thus, some heads are egg-shaped, some more round, some people have high foreheads, etc), and also in the particular bumps and dents in each skull. Despite the popularity of phrenology in the previous century, which found the reason for everything from criminal behavior to the particular nature of women (!) in the shape of the skull, there is no evidence that skull shape (and hence, brain size) has any correlation with intelligence, cognitive abilities, character, or personality. (The exception is when a particular skull feature indicates some other problem. For example, some people attribute Blaise Pascal's recurring headaches and religious visions to a cranial suture that grew into the brain rather than closing properly.) The brain is actually quite adaptable while the child grows. There was one case where the brain's ventricles, for some reason I forget, grew into a large cavity, forcing the rest of the brain structure into a relatively thin hemisphere next to the skull. This did not result in any functional problems. One American Indian tribe would keep their male infants in an odd kind of cradle that forced the head between two slanted boards, in order to give the head a flat shape. (Who knows how these things develop? Perhaps this was an early gender-based AA program.) Russell
forbes@aries.scs.uiuc.EDU (Jeff Forbes) (03/15/91)
In article <18425@cs.utexas.edu> turpin@cs.utexas.EDU (Russell Turpin) writes: >----- >In article <1991Mar8.034313.29112@ux1.cso.uiuc.edu> forbes@aries.scs.uiuc.edu (Jeff Forbes) writes: >> According to _Evolution of the Vertebrate Brain_, the adult human >> female brain (taking into account body height) is on the average 200 >> grams less than that of the adult human male brain, using the same >> scaling. What does this mean? Possibly nothing more than another odd >> medical statistic. > >You got it. > >There is quite a bit of variation in cranium shape, including >overall size, overall shape (thus, some heads are egg-shaped, >some more round, some people have high foreheads, etc), and also >in the particular bumps and dents in each skull. Despite the >popularity of phrenology in the previous century, which found >the reason for everything from criminal behavior to the >particular nature of women (!) in the shape of the skull, there >is no evidence that skull shape (and hence, brain size) has any >correlation with intelligence, cognitive abilities, character, or >personality. (The exception is when a particular skull feature >indicates some other problem. The data I quoted was not from a phrenology study. The brain mass was determined after autopsy, by weighing it. You cannot determine brain mass from the shape of the skull, but the mass may be infered from the internal volume assuming constant tissue density, which may not be appropriate. Of course, there is no substitute for actually making the measurement. Jeff Forbes "....I have not failed. I've just found 10,000 ways that won't work." Thomas Edison